Metallic sealing ring



Aug. 8, 1950 A. REIS METALLIC SEALING RING Original Filed April 5, 1946 2 Sheets-Sheet 2 I/l/ /l/ Fig-ll- INVENTOR.

ALFRED R515 A 7' TOR/VE Y Patented Aug. 8, 1950 2,518,233 METALLIC SEALINGRING rief Reis; New" York, N. Y.',- a s'si'gii-dr" 610" Entere'olamea (om-s eerl figfi 'tfie fazit'i f ctio'nal gmpertyenai ear resistance. recognition" of" this" insume'ieficy powder metallurgical methods which heve'fieceritly been developed to" agli'igli stelgidiiid; fiavej been applied lidfihi memireetufiiigfieid and'pistbn' rings fia e teen made fioiii" compressed metal powders, The

seating i'ngle are luld'ricant retaininfg? "iidiself-Ifibricatirig'j bot'tl'iey lack in memember fiioiierties and they ere particularly with? reg to s'ti'eng-tligelsti'eityi and thermal resi'stafice ififeilox to' sealing rings made of dense metal;

icles m'agl by meta-I powder metallurgical nietfi' ds and possessing a throughout porous Sfiliflfili have beenstrengthened by impregnatiiirfwitli molten metal whereby the ability of tlise I articles to.- artfidl y, absorb the-- moltenmetal Witlfih its porousaskeletonstructure has 1oeen-very lieliiful. However, as the pores are filledr with metal by the; impregnationothe article loses its lfibz ri cantlj retaining property; and" therefore its anti-frictional fumtiom and also wear resist-'- ance; It waaprimary pbd ect of the inventiomto render the-lmetali impregnation: of articles-made-by powdeifimetalliirg-"mcalmetl'iodsiusetblfor 'the' produo tioti'ofimetallics'eatliiigiring'si whi'ch c'ombiiie the d-ucemetallic sealin rii'fgs 7 which have steel? the ring into 'a dense metal body having a high strength and thermal resistance.

The invention also comprises the thus produced sealing ring.

The conversion of the main part of the ring into a dense, metal body is. efiectedby impregnation with a suitable molten metal. Y Prior to this impregnation the rings have a'uniformly porous structure, the pores forming a system of communicatin channels. Care is taken by the usual precautions used in powder metallurgy procedures to keep the surfaces of the pores pure. The molten metal is absorbed inthe pores of the rings at a minimum temperature of rapid impregnation which varies with the individual impregnating metal. 7

The impregnation results in a dense'strong product. As a very thin surface layer of between about 0.001 to 0.01 inch thickness only is excluded from the impregnation; the mechanical values of aring made in conformity with the teachings of this invention is not inferior with regard to'its mechanical and thermal properties to cast rings; therefore these sealingrings, fully comply with the mechanical and thermal requirements of. a high quality sealing ring. A sealing ring made by any known powder metallurgical method from iron or steel powder may be impregnated with metals having a suitable melting point, such as copper, tin, silver, aluminum, magnesium and their alloys. The ring also may bemade of other than ferrous .as, for instance, nickel or copper powders. The rules governing the metal impregnation of metal powder compressed articles and the utilization of the temperature ranges of rapid impregnation are known and it is not deemednecessary to dwell upon this matter in detail. 3 The invention, however, comprises special measures in connection with this impregnating step whereby the trapping of gases in the pores is avoided which would result in' an incomplete fillin of the pores. The above indicated measures are difierentiated in the various embodiments of my invention in conformity with the number and location of the ring faces to exert anti-frictional functions and to be preserved with regard to their porous lubricant retaining structure. These measures will be described in detail, as thisspecification proceeds. v a The maintenance of a throughout porous structure'and of lubricant retaining and self-lubricating property in the operating surface layer or layers of the sealing rings is secured by preventing the molten metal from penetrating into these layers. in other words, a thin'surface layer of determined depth which may vary from about 0.001 to about 0.01 inch is kept free from the impregnation by the molten metal. Due to the specific treatment, which is hereafter described, the surfaces of the pores within this superficial layer lose their wetability by the molten metal and become repulsive to the entrance of the same;

at the same time'the pores of these surface lay- 'ers remain gas permeable and allow' the free' escape of the gases which are expelled from the rin 'by the molten metalentering in the body of the ring and advancing through the same.

j The treatment which prevents the molten metal from penetration into the lubricant retaining surface layer or layers comprises applying to the selected ring faces a controlled quantity of "a non-aqueous liquid having a good wetting property to effect auniform spreading of. the same throughout the. depth controlled surface layer;

this liquid entering the pores does not fill the same but forms on the pore surfaces or pore walls a thin coherent liquid and/ or solid film; this film strongly adhering to the pore faces prevents the penetration of the impregnating metal which advances through the main body of the ring towards these surface layer or layers.

Nonaqueous liquids possessing the here required wetting, spreading and film forming property are preferably neutral oils and tars which fall inoil refineries and in the distillation plants of coal and other organic materials.

Their wetting and spreading capacity may be enhanced and controlled by the admixture of typical wetting agents of non-oxidizing nature, such as long chain alcohols, e. g. cetyl alcohol, esters and the like.

The fluidity of the liquid may be improved by the'admixture of thinners such as low molecular oils and of solvents consisting of hydrocarbons.

Oils; and tars of anthracenic ornaphthenic nature may be addedto improve the adherence of the film produced by the wetting treatment to the walls of the pores. The film deposited by the treatment'on the pore walls maybe a liquid or a solid film or a mixture thereof; its formation in these various states will greatly depend on the temperature reached during the treatment and the resulting degree of decomposition of the wetting liquid; 7 I w v r The rule which'dominates the character and the composition of the wetting and filmforminig liquid is that the same spreads equally in a thin layer of uniform thickness over the surface of the pores; the depth of liquid penetration is controlled by the quantity of liquid applied. l 1

The wetting treatment should be preferably carried-out at an elevated] temperature where the increased fluidity and surface tension .of'the liquid favor the formation of a uniform film on the surface of the pores; however, with suitable wetting liquids the treatment may be also carried out at room temperature; v p f Immediately upon the above described surface treatment the rings are either heated or if the treatment has been already' carried-out at an elevated temperature further heated to a point which is adapted for the metal impregnating step.

During the application of the wetting liquid and the heating-up period the following phenomena take place.

The volatile components of the organic wetting liquid which in the form of a film is dis-- tributed throughout the selected surface layer will gradually vaporize and displace the air on? closed within the wetted pores. As the tempera ture ascends further, decomposition will, take place of the liquid film and a solid adherent film may be established on/the walls of the pores which is'cove'red by a'liquid orpasty film; in any way this film renders the pores of the treated surface layer of the ring non-wettable by and repulsive to the entrance of the molten metal used for the impregnation of the remaining main body of the ring; on the other hand it makes-this surface layer well wettable by the lubric'antapplied 'to the operating face of the sealing ring in actual operation. V v

The wetting liquid must be so chosenthat the vapors produced prior to' or during the metal impregnation do not oxidize or otherwise attack or contaminate the porous surface or their'n pregnating metallic melt; if hydrocarbons are used, as explained above; thispurposewill be well'served. It is also important. that during or after the creation of the films on the pore a ms, ass

sees the formation: of bubbles or froth inthe pores is prevented as such occurances may ob'-- st'ruet the pores of the self-lubricating layers prevent the escape of gases from the ring during the advance of the metal impregnation; T na formation of bubbles and froth can well be prewent'ed by proper control of the surface tensiombetween the liquid and the vapors'and gases prodiiced' therefrom and by extending the vaporiration of the liquid over a wide temperature range. If: care is taken to avoidsudden increase of? temperature, the production of bubbles and froth within the pores can be definitely excluded. 'Bhkaporous: surface layers of the sealing rings pmduced by powder metallurgical processesto.

rings may be stacked for treatment upon each.

other throughout the entire treatment.

Biston ring are liquid treated attheir outer cylindricalface and the molten impregnating:

metal. is applied to the inner cylindrical face"; in the treatment of rod type rings, rings for: stuffing; boxes and the like, this treatment. is reversed.

For. the production of rings having lubricant retaining, surface layers in one cylindrical and in:

both. plane. faces; the inner cylindrical face is. previously metal coated.

Severalmethods for. the treatment of the. ring faces: and for the impregnation of the remainingJmainpa-rt. of the. rings with molten metal are iirdetailv described in the following and illustrat'edllby. means. of the accompanying drawings.

In the drawings:

E12,. 1 isa diagrammatical vertical cross-sectionofa piston ring of the external type located in ar piston with its outer cylindrical lubricant retaining, self-lubricating face adjacent to the cylinder wall, the cylinder and the piston being; only partly shown,

Fig; 2l'is a vertical cross-section similar to that of" Fig; 1' of the ring. with lubricant retaining; selflubricating surface layers being shown as appliedfto, the two plane faces as well as to. the cylindrical outer face,

Fig, 3is a d'i'agrammatical vertical cross-section of" ase'aling ring of the internal type located in Stufiii'ig. box with its inner cylindrical selfl'iib'ricating face adjacent to an inner cylindrical guidemember the latter as well as the stuffing B'orbeing only partly shown,

Figsml, 5, 6 are oliagraminatical. vertical crosssectibns of one side of" a piston ring shown in Figgri'n. the course of its main manufacturing ep Figs. 7, 8, 9', 10 are. diagrammatical'views of a m'odificatiomof the manufacturing steps for the production ofa sealing ring shown in Fig. 2,

11' is a vertical cross-section of a chamberforth'etreatment ofa ring stack,

Fig. 12 is a horizontal cross-section on line Ib -r2 of Fig; 11,

Fig. 13 is. a diagramillustrating the temperatiirefgradient' createdduring. the impregnation of. tlie ri'ng shown in Fig. 1.

The" pistonring of the external type" shown in Fig; 1' is iirth'e'usual manner located in a circular recess 1* of a' piston 21' the lubricant retaining cylindrical porous outsidesurface' layer which is in slidingcontact' with cylinder 3 during the displacement of the piston and situated at theout'er cylindrical face ['11- is indicated by' numeral 4 andthe metal impregnatedmainpart attire-ring by-numeral- 5; the ratioof thickness of layer-4' andmaimbody shownin the drawing dbes not correspond to the actual situation; as layer" is thinner than shown in theidrawing. Th'e innen cylihdrioalface of theringis denominated by'numoral andthe plane faces by numeral 1 the numerals 61 T- andlo denonnnating'the various. faces of external sealing rings are maintained throughout the Figures. 13 one: side: of this ring. is 1 cm an: enlargedi scale: shown: in: Big 2; V

2.- illustrates a; sealing. ring having" addia tlonal lubricant: retaining: self-lubricating layers to which; are applied; to" the; two: plane" races. ll of the ring:.

Fig: 3 showsza; sealing'rringz of the-internal; on rod type; the ring is located in a circular recess' 5-. of stuffing; box 8; The selfelubricating fporous inside layer,, which. during. the: operation: of the: ring is inzslidingcontact: with the inner: cylindrlr calguide'membersi H. is.'denominatedby numeral? 4b.- and the metal impregnated. main; part" of-rtlre ring: with numeral I3.

Figs-.- 4; 5, 6 arediagrammatical' vertical; sec. tional elevations-ofone- SideOfIaz piston ring; duning; the-progressof it treatment.

Fig. 4 illustrates the uniformlyporous ring: after its manufacture by powder metallurgy operations.

Fig; 5 illustratesthe same ring after the appli-' cation ofthe wetting liquid: to'its outside cyline drical. face l0. and the creation of anadherent; film torthe porexfaces of. the surfacerlayer 4:.

Fig. 6 indicates the advance of: the metal: meg-nation. l6.-which takes: place in the: direction of the arrow from thecylindrical inside: face: E of the: ring; towards its outer face: Ml.-

Figs. 7- to loare diagrammaticalverticahsecs tionalviews showing: the manufacture of" aiseaie ing ring provided with alubricant retainin'gxelfe lubricating porous-layeratits cylindrical-outside face andatitsiboth plane faoess Fig. 7 illustrates one side of. the; poroussrinsz after itsmanufacturefrom aimetal powdeiz; In accordance with. Fig 8- an adherent metallic" coating [4 is applied to its inner face: 6::byrany customary. dry metallizing method. The metal used for the formation: ofmetal coat;- M may-she the same as the one" later used for: the? metallic i'mpregation of the a ring; however, also a differenti metal. may be chosen to seal. uptheinnercringa face- 6.; the. metal: which. is used I for this coating and sealing stepshould-havera meltinggpointlto become liquid during the -metal impregnationro'fi' thering'. This embodimentlof the inventiomiwilt be described in detail in. a: later part of: this specification; Fig, 9. shows the same: ring; after the. creation. of. the; lubricant retaining surface: layers-- 4-,- Aa. and Fig; 10- indicates the: adVEZHCE OYF. theimpregnatingmetal" I51 from face Sltowards the lubricant retaining; surface layers: 4;. 412:

An apparatus. for producing sealing: rings iir: accordance. with. the invention is. shown in: 11 and. 12..

The: apparatus comprises a preferablycyline drical .vertical treatingchamber A built ofaasuitable refractory material l9 and encased by a metal'housing 20. The chamber which is opem at its upper endis supported on a circular base 2 I.

by a holder which consists of two rings 25 connected by three rods 26; this carrier is vertically movably suspended by chain 21.

By means of this holder the column 24 of stacked rings can be lowered at a controlled speed through the inner space of the treating chamberA.

A plurality of nozzle provided tubes 28 is located. directly above the treating chamber A at the outside circumference of ring column 24 for the application of the Wetting liquid to the outer cylindrical face of the ring stack. The tubes 28 conducting the wetting liquid to nozzles are provided with valves 29 to control the supply of the wetting liquid. v

A tube 30 conducting the impregnating metal and provided at its upper end with a plurality of radial nozzle-provided arms 31 is located in the lower portion of chamber A in such a manner that the descending ring column 24 must pass along the outlets of arm 3i. The ring column is shown in full lines during its passage along tubes 28 and in dotted lines during its passage along the outlets of the arms 3!. Tube 30 supplies the molten impregnating metal to the inner face of the ring stack.

The treating zones to be successively traversed by ring stack 24' are indicated by numerals 32,

33; 34, numeral 32 indicating the preheating zone, numeral 33 the wetting zone, numeral 34 the heating zone and numeral 35 the metal impregnating zone.

The heat required for the treatment is supplied by the electrical resistors 23.

A container 36 is located underneath chamber A for the accumulation of excess molten metal not absorbed by the ring stack during its passage along the ends of tubular arms 3!. b b

An adjustable refractory valve plug 38 is provided in tube 30 to control the supply of the pregnating metal.

1 .The production of external pistons by means of the above described treating chamber is carried out as follows: i

The rings compressed from a suitable metal powder into a throughout porous body are stacked in superimposed relation on holder 25, 36; see also Fig. 11, to form column 24; the inner and outer cylindrical faces 6, IU of' the rings are accordingly exposed to successive treatments.

The holder 25, 26 is at the commencement of the treatment suspended by means of chain 2! in the preheating zone 32 above the upper end of the cylindrical chamber A. g y

- Heat is applied by the resistor element 23, the highest temperature being created in the center section of the chamber, where the heating zone 34 and the upper part of the impregnating zone 35 are located; the temperature decreases gradually-toward the upper open end of the chamber; the non-oxidizing or inert gases supplied by tubes 22 and escaping from I the upper end of the chamber protect the ring stack against oxidation.

"The preheated ring stack 2 3 is lowered from the preheating zone 32 into and through the Wetting zone 33. A controlled quantity of the above deheated previous to the metallic impregnation is scribed wetting liquid is applied by spray tubes 28 to the outer cylindrical faces [0 of the ring stack, creating the previously described surface layer which is not wettable by molten metal but easily wettable by lubricants. V

By proper adjustment of the temperature, by suitable selection of the wetting liquid and particularly its viscosity and the control of the suply of the wetting liquid, the desired depth of the surface layer, the formation of an adherent liquid and/ or solidfilm on the pore faces and the pre. vention of froth and bubbles in the pores can be easily attained. a

The ring stack is lowered through zone 33 and passed into heating zone 34 and finally into the metal impregnating zone Here the molten metal is supplied by tubes 33, 3| to the inner cyl-' indrical faces 6 of the ring stack.

lhe progress of the impregnation can be controlled by adjustment of the lowering speed of the holder 25, 26 and of the supply of the molten metal; any surplus metal supplied to the ring stack and prevented from entering the Wetted and film coated outer cylindrical surface layer 4 will be collected in container 36, which may be heated to keep this metal in a molten state.

The above described treatment can be easily modified to suit the purpose of the manufacture of different types of sealing rings.

The individual steps of the treatment are performed in direct succession to save time and to avoid undesirable chemical reactions on the surfaces of the pores.

Care must be taken, as already stated above, to prevent the formation of vapor or gas bubbles in the pores, as this would impede the escape of gases and perhaps lead to the contamination of the pores beyond the desired depth of penetration.

The temperature to which the stacked rings are important; the stacked rings, when brought in contact with the metallic melt, should be heated to a temperature just below the temperature of rapid impregnation. This latter temperature is located slightly above the melting point of the metal, or if the molten metal is very viscous, somewhat higher and to a point where fluidity becomes sufficient for a rapid flow through the narrow pores. 7

On the other hand, the metallic melt to be applied to the rings is heated to sufficiently high temperature to raise the temperature of the rings in a short time to the temperature for the rapid impregnation; in other words, the temperature of the treatment is so controlled that the rings enter the impregnating zone 35 with a temperature which is below the temperature at which rapid absorption of the impregnating metal 00- curs; the impregnating metal itself heats the ring stack up to the temperature of rapid impregna amazes layer a during the advance 'nf the. impregnating metal. isillustrated in the; diagram shown in Fig.

1%, representing a section'of'one. side of the rin temperature to which'the ring stack has been heated in zone 34. prior to its impregnation in gone. 35 is denominated by t, the temperature of rapid im-pregnation'which is higher than t by and the temperature of the impregnating metallic melt whichyas. previously explained; is higher than the temperature of rapid impregnatic r v iq a The. difierence between the-temperatures t and t '.;i $o ;adiusted that the ring stack by the ad.- vance of the-molten; metal is. heated to the ap piseximate temperature t the increase of the temperature in the, stack to-the temperature t thereforeis a forerunner to the advance of the metal; the desired temperature gradient towards surface layer 4 is established in this manner.

The temperature 1& and 2& are represented in. the. diagram. by; horizontal. lines- The metal is, as previously described, applied to the inner cylindrical. face-6 pi the ring stack and advances toward the outer surface layer 4 which hasqbcen rendered repulsive to metal impregnation.

The vertical lines r r 1 represent the radial distances trauersfed by advancing metal; these. distances decrease with the time in accordance with the gradually .slowed down. advance of themetal. H k Y Curve I- shows the temperature distribution curve flt'er the advancement of the metal to the radiusr At thetime of curve 1', all the pores within the radiuszr have been filledv with metal, but not. be.- yond that radius.

At the time of temperature distribution according to curve 2, impregnation has progressed to the radius 1' In this manner the impregnation proceeds until all pores of the ring stack are metal filled with the exception of these located in the outside surface layer 4.

Due to the maintenance of the temperature gradient demonstrated in Fig. 13, a steady metal advance is obtained, the trapping of gases in the pores is prevented and a thorough uniform filling of the pores is accomplished. The impregnation advances in direct dependance upon the temperature distribution indicated by the curves I, 2, 3 and so forth until all pores of the not treated main body of the ring stack are metal filled.

Sealing rings of the internal or rod type are treated in the form of stacks by a similar procedure as described above. In this case the spray nozzles for the wetting liquid Will be placed at the inside of the ring column and the molten metal will be applied to the outside. I

The above described embodiments of the invention result in the production of sealing rings having a porous superficial layer at one cylindrical face.

However, the invention may be equally well used for making sealing rings having one cylindrical and two plane faces converted into lubricant retaining self-lubricating surface layers.

The procedure used for this embodiment of the invention will now be described.

In this case the one cylindrical face to be used for the impregnation with molten metal is protected against the treatment with the wetting liquid; therefore the process is commenced by closing the pores of the inner face of the ring stack with metal; this purpose is accomplished 10 by metallization or by another suitable operation, whereby a thin coherent and adherent metallic coating is applied which completely closes the inner face of the ring stack.

The metal used for this purpose may be the same as the one later used for the metallic impregnation or it may be a different metal; how ever, it must be sufiiciently fluid at the temperature of themetallic impregnation.

As the molten metal applied for impregnation advances into the ring, the metal which has. been used for closing the pores will act as a pacemaker for the impregnating metal; its composition there fore may be selected to assure an easy union with the impregnating metal, a lowering-of the melting point and a higher fluidity at the fin, pregnating temperature. These purposes are obtained by the coating? metal, whereas the metallic. composition usedfor impregnation, is selected with a viewof its me.-I chemical and thermal properties in the solid state and of the creation of easy impregnating conditions.

- The application of the metal coating to the inner ring face is carried-put with the stacked formation of the'rings.

. After. the innercircular face of the ring stack has. been metal coated and closed, the rings areunstaeked and all other facesare subjected to the above described treatment with the wetting liquid; thereuponthe impregnation is effectedthrough the metal coated inner face. The metallic impregnation may be effected inany suitable manner, for instance by immersion: of. the liquid treated rings into a bath of molten metal. The. p ress of the. work in accordance with the above stated second embodiment of the invention is schematically illustrated in Figs. '7-10.

Fig. 7 shows a vertical sectional elevation of one side of the individual porous ring before the commencement of the treatment, Fig. 8 after the closure of its inner face 6 by a metal coating I 4, Fig. 9 after the treatment of the other three faces with the wetting liquid and the creation of metal repellant surface layers 4, 4a and Fig. 10 shows the progress of the metallic impregnation in the direction towards the outer surface layer 4 of the individual ring and the two plane surface layers 2a.

In this em-bOdiment of the invention only the inner cylindrical face 6 is accessible to the entrance of molten metal, therefore a trapping of gases in the pores cannot occur. The impregnation will advance from face 6 towards all the other faces which remain open for the escape of the gases, the latter being expelled from the pores of the ring by the advancing metallic melt.

In applying this modification of the invention to rings of the internal or rod type, the latter are stacked and metallized at the outer cylindrical face l0, then unstacked and carried through the above described steps of wetting liquid treatment, heating and metallic impregnation.

The sealing rings made in accordance with this invention combine the superior lubricant retaining self-lubricant anti-frictional and wear resistance properties of porous articles made by powder metallurgical methods with the high elasticity, permanence of tension, static strength, creep resistance, toughness and heat resistance of metallic bodies.

The invention is described by way of example only and equivalent operations and means may be used without departing from the scope of the attached claims.

What I claim is:

1. A method for the manufacture of a sealing ring comprising producing the rin by a powder metallurgical process as a coherent article having a throughout porous skeleton structure, applying at an elevated temperature to at least one surface of the ring a controlled quantity of a non-aqueous organic wetting liquid, partly decomposing the liquid and covering the pores of said surface layer with a film formed of the decomposition products which'is repulsive to impregnation with a molten metal, preserving at the same time the porous skeleton structure of said surface layer and creating a lubricant retaining self-lubricatin face of unrestrained gas permeability and impregnating the remaining main part of the ring with molten metal through at least one of the "untreated faces of the ring.

2. A method for the manufacture-of a sealing ring comprising producing the ring by a powder metallurgical process as a coherent article having a throughout porous skeleton structure, metal coating'one circular face, applying to the other circular. and to the plane faces of the ring a controlled quantity of a non-aqueous organic wetting liquid, producing thereby a surface layer,

having the pore walls covered with a film which 7 renders the said layers repulsive to impregnation with a molten metal and preserving at the same time theporous skeleton structure of said surface laycisfcreating thereby lubricant retaining selflubricating faces of unrestrained gas permeability andimpregnating the remaining part of the ring by its immersion into molten metal.

'3. A method for the manufacture of a sealing layer which is repulsive to impregnation with molten metal, preserving therein the porous skeleton structure and creating a lubricant retaining self-lubricating face of unrestrained gas permea bility, raising the temperature of the ring stack and moving the same into a zone for the impregnation with a molten metal, applying to the oppo-" site circular face'of said ring stack a stream of molten metal, advancing the molten metal towards said porous surface layer, filling thereby the pores of the remaining main portion of the rings with metal, expelling the gaseous contents of the rin stack through the said porous surface layer and subdividing the treated ring stack into individual rings.

ALFRED REIS,

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,159,763 Hensel May 23, 1939 2,402,950 Culver et al. Jul 2, 1946 2,422,439

Schwarzkopf June 1'7, 194'? 

1. A METHOD FOR THE MANUFACTURE OF A SEALING RING COMPRISING PRODUCING THE RING BY A POWDER METALLURGICAL PROCESS AS A COHERENT ARTICLE HAVING A THROUGHOUT POROUS SKELETON STRUCTURE, APPLYING AT AN ELEVATED TEMPERATURE TO AT LEAST ONE SURFACE OF THE RING A CONTROLLED QUANTITY OF A NON-AQUEOUS ORGANIC WETTING LIQUID, PARTLY DECOMPOSING THE LIQUID AND COVERING THE PORES OF SAID SURFACE LAYER WITH A FILM FORMED OF THE DECOMPOSITION PRODUCTS WHICH IS REPULSIVE TO IMPREGNATION WITH A MOLTEN METAL, PRESERVING AT THE SAME TIME THE POROUS SKELETON STRUCTURE OF SAID SURFACE LAYER AND CREATING A LUBRICANT RETAINING SELF-LUBRICATING FACE OF UNRESTRAINED GAS PERMEABILITY AND IMPREGNATING THE REMAINING MAIN PART OF THE RING WITH MOLTEN METAL THROUGH AT LEAST ONE OF THE UNTREATED FACES OF THE RING. 